1. Field of the Invention
The present invention relates to a wire saw having improved cutting efficiency and accuracy by swing row of wires in pushing a workpiece against the row of wires reciprocating or traveling in one direction at high speed to cut the workpiece and more particularly to a wire saw in which occurrence of tension fluctuations in wires at a time of swinging of the row of wires is prevented to prevent occurrence of cuts of the wire to obtain stable traveling performance.
2. Description of the Related Art
Conventionally, in a wire saw in which a row of wires are swung in cutting a workpiece, as shown in FIG. 9, wire A drawn out from a feed side reel 1 is led via a feed side traverser 3 driven by a motor 2 and a plurality of guide pulleys 4 to a tension mechanism 7 formed of an encoder 5 and a tension arm 6, a load cell 8 for measuring tension in the wire A, and a plurality of guide pulleys 9 and then wound around three work rollers 11 mounted to a swinging disk 10 many times to form a row of wires. Then, the wire A passes through a plurality of guide pulleys 12, a load cell 13 for measuring tension of the wire A, a tension mechanism 16 formed of an encoder 14 and a tension arm 15, a plurality of guide pulleys 17, and a retrieving side traverser 19 driven by a motor 18 and is taken up by a retrieving side reel 20.
Each of the work rollers 11 is formed in its outer periphery with grooves and a workpiece fixing table 21 is disposed to be properly moved up and down by driving means (not shown) right above an upper row of wires wound by utilizing the grooves around an outer periphery between the work rollers 11 to thereby push down a workpiece B mounted to a lower face of the workpiece fixing table 21 toward the row of wires.
As the above-described wire saw, there are a loose abrasive grain wire saw in which slurry liquid including hard abrasive grains such as SiC, diamond, and the like is supplied to a vicinity of a workpiece cutting position of the row of wires by a nozzle 22 and a fixed abrasive grain wire saw for cutting by using the wire A to which diamond grains are fixed through resin or the like and while supplying coolant to the workpiece cutting position of the row of wires.
The vertical swinging disk 10 mounted with the work rollers 11 are rotatably supported on a machine base 23 through a cross roller bearing 24 and is rotated in a reciprocating manner through a constant angle at a time of cutting of the workpiece and is fully rotated at a time of winding of the wire about the work rollers by a driving motor 25 through a pulley and a belt provided to a rear end.
A swinging mechanism of the row of wires swings the row of wires in a reciprocating manner through a constant angle at a time of cutting of the workpiece by rotating the swinging disk mounted with the work rollers in a reciprocating manner by using the different motor 25 from a spindle for driving the work rollers for rotation. In the mechanism, the wire A comes in contact with the workpiece B in an arc shape to thereby reduce contact resistance to improve bringing in of the slurry liquid to enhance cutting performance.
Conventionally, to guide the wire A to the work rollers 11 of the above-described kind of wire saw, the feed side guide pulleys 9 for guiding the feed side wire going into the work rollers 11 to the work rollers 11 and the retrieving side guide pulleys 12 for guiding the retrieving side wire going out of the work rollers 11 to an outside are fixed and disposed in positions outside and isolated from an axial center of rotation of the swinging disk 10 (see Japanese Examined Patent Publication No. 6-35107, for example)
In a structure in which the feed side guide pulleys 9 and the retrieving side guide pulleys 12 are fixed and disposed in the positions outside and isolated from the axial center of rotation of the swinging disk 10 with respect to the work rollers 11, distances between the work rollers 11 and the feed side guide pulleys 9 and the retrieving side guide pulleys 12 fluctuate in swinging of the row of wires and therefore the wire A is pulled or loosened.
Moreover, in recent cutting of a silicon ingot or the like, there are tendencies to reduce a thickness of a wafer to increase the number of wafers obtained from a work ingot and to reduce a diameter of the wire A to minimize cutting loss from a viewpoint of reduction in manufacturing cost. Therefore, challenges in the wire saw are to reduce the diameter of the wire A and to increase a linear velocity of the wire A from a viewpoint of improvement in manufacturing efficiency.
However, in the swinging mechanism in the above-described prior-art wire saw, fluctuations in the wire tension are large in swinging of the row of wires. If the wire diameter is reduced, a load on the wire increases in swinging and the wire may be cut in some cases.
Moreover, in increasing the linear velocity of the wire, the wire may be broken in the swinging in some cases similarly to the above case.
Furthermore, in a wire saw in which work rollers are directly driven in normal and reverse directions to cause wire to reciprocate at high velocity, it is conceivable that rotation of a wire reel is caused to follow tension fluctuations in the wire by a driving motor for the wire reel. However, such a method requires a high-precision driving motor, which results in high cost.
In the fixed abrasive grain wire saw, there is a tendency to increase a swinging angle so as to enhance the cutting performance, which results in large tension fluctuations in the wire at the time of swinging.